Elsevier

World Neurosurgery

Volume 98, February 2017, Pages 538-545
World Neurosurgery

Original Article
Bifurcation Location Is Significantly Associated with Rupture of Small Intracranial Aneurysms (<5 mm)

https://doi.org/10.1016/j.wneu.2016.11.055Get rights and content

Background and Objective

Patients with small (<5 mm) unruptured intracranial aneurysms (UIAs) are at risk of subarachnoid hemorrhage, but risk assessment of these patients remains controversial in daily clinical practice. We aimed to identify the risk factors of aneurysmal rupture in these patients.

Methods

We retrospectively analyzed consecutive patients with small UIAs who were admitted to our center between February 2009 and December 2014. The enrolled patients were divided into ruptured and unruptured groups. The risk factors for aneurysmal rupture were determined using multivariate logistic regression analysis.

Results

A total of 548 patients with 618 small intracranial aneurysms (267 ruptured and 351 unruptured) were included. Univariate analysis showed that rupture of small aneurysms was related to sex, age, smoking, hypertension, aspect ratio, size ratio, irregular shape, aneurysm width, height, and neck diameter, and location at bifurcation or posterior circulation. Multivariate logistic regression showed that rupture was associated with bifurcation location (odds ratio [OR], 5.409; 95% confidence interval [CI], 3.656–8.001; P < 0.001), size ratio (OR, 3.092; 95% CI, 2.002–4.774; P < 0.001), location (OR, 2.624; 95% CI, 1.428–4.824; P = 0.002), hypertension (OR, 1.698; 95% CI, 1.1140–2.527; P = 0.009), and age at diagnosis of UIA (OR, 1.826; 95% CI, 1.225–2.723; P = 0.003).

Conclusions

This study showed that 70.4% of small ruptured intracranial aneurysms (<5 mm) were located at parent artery bifurcations and that bifurcation location was a significant independent factor for the risk of rupture of small UIAs (<5 mm). Prophylactic treatment should be recommended for small UIAs in this location.

Introduction

The prevalence of unruptured intracranial aneurysms (UIAs) is 1%–7%.1 The most serious damage caused by UIAs is a result of subarachnoid hemorrhage (SAH), which has a 30-day mortality of 40%.2 The rupture risk is known to increase with increasing aneurysm size.1, 3, 4 Thus, most small UIAs (<5 mm) are believed to be associated with a low risk of rupture. However, several studies5, 6 have reported the rupture of small aneurysms. Kassell et al.7 assessed 1092 cases to analyze the size distribution of ruptured aneurysms and found that 13% of ruptured aneurysms were <5 mm in diameter. A study by Kashiwazaki et al.8 clearly showed that approximately 30% of ruptured intracranial aneurysms (RIAs) were small (<5 mm) and that some small UIAs also had a risk of rupture.9, 10, 11, 12

Several previous studies have investigated the risk factors of rupture in patients with small UIAs. In the Japanese Small Unruptured Intracranial Aneurysm Verification study,9 the rupture of small UIAs was found to be related to age, hypertension, and the presence of multiple aneurysms. However, those prospectively studied groups did not include small aneurysms that had been previously treated, and many patients with small UIAs that may have been at high risk of rupture were treated and were not enrolled into the studies. Kashiwazaki et al.8 found that size ratio (SR) might predict the risk of rupture in small UIAs, but the potential risk factors of rupture included in that multivariate analysis may be insufficient, and no systematic analyses of the risk factors for rupture of small UIAs are available.

We tried to analyze as many factors associated with the rupture of small IAs as possible to investigate the predictors of rupture in a large cohort of patients with small UIAs and RIAs.

Section snippets

Study Design and Ethics

This was a retrospective study. The design was approved by the review committee of Beijing Tiantan Hospital, and informed consent was obtained from all participants.

Patient Selection

We retrospectively reviewed consecutive patients who attended our institution with small intracranial aneurysms (IAs) (<5 mm) from February 2009 to December 2014. All patients in this study were examined using three-dimensional rotational angiography. All patients with SAH were examined using computed tomography. All patients

Study Population

A total of 548 consecutive patients with 618 small aneurysms, including 267 RIAs and 351 UIAs, were included in this study. Seventy-six patients were excluded for the following reasons: the location of the ruptured aneurysm could not be identified (n = 20); inability to find the digital subtraction angiography image (n = 12); fusiform, traumatic, or dissecting aneurysm (n = 16); or aneurysms that were related to cerebral arteriovenous malformation, arteriovenous fistula, or moyamoya disease (n

Discussion

In this study, the main finding was that location at parent artery bifurcations in the circle of Willis or in the posterior circulation, higher SR, younger age (<50 years), and hypertension were risk factors of rupture in small UIAs.

Conclusions

This study showed that 70.4% of small RIAs (<5 mm) were located at parent artery bifurcations and bifurcation location was a significant independent factor for the risk of rupture of small UIAs (<5 mm). Prophylactic treatment should be recommended for small UIAs (<5 mm) in this location. Higher SR, location in the posterior circulation, younger age (<50 years), and hypertension were also independent factors associated with the risk of small UIA rupture, and more prospective studies are needed

Acknowledgments

A.L. conceived and designed the experiments. X.F. and W.J. performed the experiments. X.F. and H.K. analyzed the data. Z.Q., P.L., X.W., W.X., Y.L., and C.J. contributed reagents, materials, and analysis tools. X.F. and W.J. wrote the article. Z.W. revised the manuscript.

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    Conflict of interest statement: This research was supported by the Natural Science Foundation of Beijing, China (no.7142032) and Specific Research Projects for Capital Health Development (2014-3-2044).

    Xin Feng and Wenjun Ji contributed equally to this work.

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